RU2665228C1 - Audio encoder and decoder for interlace waveform encoding - Google Patents

Abstract

FIELD: data processing.SUBSTANCE: invention relates to encoding and decoding and is intended for performing high-frequency reconstruction of an audio signal. These methods and apparatus for decoding and encoding audio signals, in particular a decoding method, include receiving a waveform encoded signal having a spectral composition corresponding to a subset of the frequency band above the transition frequency. Waveform encoded is interleaved with a parametric high-frequency reconstruction of the audio signal above the transition frequency, thus, an improved reconstruction of the high-frequency bands of the audio signal is achieved.EFFECT: providing improved reconstruction of transients and tonal components in high-frequency bands.20 cl, 9 dwg

Description

FIELD OF THE INVENTION

The invention disclosed herein generally relates to encoding and decoding an audio signal. In particular, it relates to an audio encoder and an audio decoder for performing high-frequency reconstruction of audio signals.

State of the art

Audio coding systems use different methodologies for encoding an audio signal, for example, wave coding itself, parametric spatial coding, and high-frequency reconstruction algorithms, including a spectral band copy (SBR) algorithm. The MPEG-4 standard combines waveform coding with SBR audio signals. More specifically, the encoder can perform waveform coding of an audio signal for spectral bands up to a transition frequency and encode spectral bands above a transition frequency using SBR coding. The waveform-encoded portion of the audio signal is then transmitted to the decoder together with the SBR parameters determined by SBR encoding. Based on the waveform-encoded portion of the audio signal and SBR parameters, the decoder then reconstructs the audio signal in the spectral bands above the transition frequency, as discussed in a review article by Brinker et al., An overview of the Coding Standard MPEG-4 Audio Amendments 1 and 2: HE- AAC, SSC, and HE-AAC v2, EURASIP Journal on Audio, Speech, and Music Processing, Volume 2009, Article ID 468971.

One problem with this approach is that strong tonal components, i.e. strong harmonic components, or any component in high spectral bands that are poorly reconstructed by the SBR algorithm, disappear in the output signal.

For this reason, the SBR algorithm implements a procedure for detecting missing harmonics. Tonal components that cannot be properly restored by high frequency SBR reconstruction are identified on the encoder side. Information about the frequency position of these strong tonal components is transmitted to the decoder, where the spectral compositions in the spectral bands where the missing tonal components are located are replaced by the sinusoids generated by the decoder.

The advantage of detecting missing harmonics provided in the SBR algorithm is that it is a solution of a very low bit rate, since, to simplify somewhat, it is only necessary to transmit to the decoder the frequency position of the tonal component and its amplitude level.

The disadvantage of detecting the missing harmonics of the SBR algorithm is that it is a very crude model. Another disadvantage is that at a low transmission rate, i.e. when the number of bits that can be transmitted per second is small and, as a result, the spectral bands are wide, a large frequency range will be replaced by a sine wave.

Another drawback of the SBR algorithm is that it tends to blur the transients occurring in the audio signal. Typically, leading echo and lagging echo of the transient occurs in the SBR reconstructed audio signal. Thus, there is room for improvement.

Brief Description of the Drawings

Hereinafter, illustrative embodiments will be described in more detail and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a decoder according to exemplary embodiments;

FIG. 2 is a schematic diagram of a decoder according to exemplary embodiments;

FIG. 3 is a flowchart of a decoding method according to exemplary embodiments;

FIG. 4 is a schematic diagram of a decoder according to exemplary embodiments;

FIG. 5 is a diagram of an encoder according to exemplary embodiments;

FIG. 6 is a flowchart of an encoding method according to exemplary embodiments;

FIG. 7 is a diagram of a signaling circuit according to exemplary embodiments; and

FIG. 8a-b is a schematic illustration of an interleaver according to exemplary embodiments.

All drawings are simplified and, in general, show only parts that are necessary to explain the invention, while other parts can be excluded or considered optional. Unless otherwise indicated, like reference numerals refer to like parts in different figures.

DETAILED DESCRIPTION OF THE INVENTION

In view of the foregoing, the objective is to provide an encoder and a decoder and corresponding methods that provide improved reconstruction of transients and tonal components in high frequency bands.

I. Overview - Decoder

As used herein, the term “audio signal” can mean an audio signal itself, an audio portion of an audio-visual signal or a multimedia signal, or any of them together with metadata.

According to a first aspect, exemplary embodiments provide decoding methods, decoding devices, and computer program products for decoding. The proposed methods, devices and computer software products, in General, can have the same features and advantages.

According to exemplary embodiments, there is provided a decoding method in an audio signal processing system, comprising: receiving a first waveform-encoded signal having a spectral composition up to a first transition frequency; receiving a second waveform encoded signal having a spectral composition corresponding to a subset of the frequency range above the first transition frequency; receiving parameters of high-frequency reconstruction; performing high-frequency reconstruction using the first waveform-encoded signal and high-frequency reconstruction parameters to generate a frequency-expanded signal having a spectral composition above the first transition frequency; and interleaving the frequency-expanded signal with a second waveform encoded signal.

As used herein, the term “waveform encoded signal” should be interpreted as a signal encoded by directly quantizing a waveform representation; most preferably quantization of the frequency conversion lines of the input waveform. This is the difference from parametric coding, where the signal is represented by variations of the generalized signal attribute model.

Thus, the decoding method involves the use of waveform encoded data in a subset of the frequency range above the first transition frequency and their interleaving with a signal reconstructed at a high frequency. Thus, important parts of the signal in the frequency band above the first transition frequency, for example, tonal components or transients, which are usually poorly reconstructed by parametric high-frequency reconstruction algorithms, can be encoded in waveform. As a result, the reconstruction of these important parts of the signal in the frequency band above the first transition frequency is improved.

According to exemplary embodiments, the subset of the frequency range above the first transition frequency is a sparse subset. For example, it may contain many isolated frequency intervals. This has the advantage that a small number of bits are used to encode the second waveform encoded signal. However, due to the presence of many isolated frequency intervals, tonal components, such as single harmonics, of an audio signal can be well captured by a second waveform encoded signal. As a result, improved reconstruction of the tonal components for the high frequency bands is achieved with low bit consumption.

As used herein, the term “missing harmonics” or “single harmonics” means any arbitrary strong tonal portion of the spectrum. In particular, it should be understood that the concept of “missing harmonics” or “single harmonics” is not limited to harmonics of the harmonic series.

According to exemplary embodiments, the second waveform encoded signal may represent a transient in the audio signal to be reconstructed. The transient is usually limited to a short time range, for example, about a hundred time samples at a sampling frequency of 48 kHz, for example, a time range of the order of 5 to 10 milliseconds, but can have a wide frequency range. Therefore, to capture a transient, a subset of the frequency range above the first transition frequency may comprise a frequency interval between the first transition frequency and the second transition frequency. This has the advantage that improved transient reconstruction can be achieved.

According to exemplary embodiments, the second transition frequency varies as a function of time. For example, the second transition frequency may vary in a time frame set by the audio processing system. Thus, a short time range of transients can be calculated.

According to exemplary embodiments, the high frequency reconstruction step comprises performing a spectral band copy, SBR. High-frequency reconstruction is usually carried out in the frequency domain, for example, in the field of pseudo-quadrature mirror filters, QMF, consisting, for example, of 64 subbands.

According to exemplary embodiments, the step of interleaving the frequency spread signal with a second waveform encoded signal is in the frequency domain, for example, in the QMF region. Usually, to simplify the implementation and improve control of the time and frequency characteristics of two signals, the interleaving is carried out in the same frequency domain as the high-frequency reconstruction.

According to exemplary embodiments, the first and second waveform encoded signals, when received, are encoded using the same modified discrete cosine transform, MDCT.

According to exemplary embodiments, the decoding method may comprise adjusting the spectral composition of the frequency-expanded signal in accordance with high-frequency reconstruction parameters to adjust the spectral envelope of the frequency-expanded signal.

According to exemplary embodiments, the interleaving may comprise summing a second waveform encoded signal with a frequency-expanded signal. This option is preferred if the second waveform encoded signal represents tonal components, for example, when a subset of the frequency range above the first transition frequency contains a plurality of isolated frequency intervals. Summing a second waveform encoded signal with a frequency-expanded signal mimics the parametric harmonics known from SBR and allows the SBR to copy the signal to be used to avoid replacing large frequency ranges with a single tonal component by mixing it at a suitable level.

According to exemplary embodiments, the interleaving comprises replacing the spectral composition of the frequency-expanded signal with the spectral composition of the second waveform encoded signal in a subset of the frequency range above the first transition frequency, which corresponds to the spectral composition of the second waveform encoded signal. This embodiment is preferred when the second waveform encoded signal represents a transient, for example, when a subset of the frequency range above the first transition frequency may thus comprise a frequency span between the first transition frequency and the second transition frequency. Replacement is usually performed only for the time range covered by the second waveform encoded signal. Thus, it is possible to replace as little as possible, but still sufficient to replace the transient and potential temporal erosion present in the frequency-expanded signal, and interleaving is thus not limited to the length of time indicated by the SBR envelope time grid.

According to exemplary embodiments, the first and second waveform encoded signals may be separate signals, in the sense that they are individually encoded. Alternatively, the first waveform encoded signal and the second waveform encoded signal form the first and second signal portions of a common, jointly encoded signal. The latter alternative is more attractive in terms of implementation.

According to exemplary embodiments, the decoding method may comprise receiving a control signal comprising data relating to one or more time bands and one or more frequency bands above the first transition frequency for which a second waveform encoded signal is available, wherein the frequency-interleaved phase a signal with a second waveform encoded signal is based on a control signal. This has the advantage of providing efficient interleaving control.

According to exemplary embodiments, the control signal comprises at least one of a second vector indicating one or more frequency ranges above the first transition frequency for which a second waveform encoded signal is available for interleaving with a frequency-expanded signal, and a third vector, indicating one or more time ranges for which a second waveform encoded signal is available for interleaving with a frequency-expanded signal. This allows you to conveniently implement the control signal.

According to exemplary embodiments, the control signal comprises a first vector indicating one or more frequency ranges above the first transition frequency to be parametrically reconstructed based on high frequency reconstruction parameters. Thus, the frequency-expanded signal can be given priority over the second waveform-encoded signal for certain frequency bands.

According to exemplary embodiments, a computer program product is also provided comprising a computer-readable medium with instructions for implementing any method of decoding the first aspect.

According to exemplary embodiments, there is also provided a decoder for an audio signal processing system, comprising: a receiving unit configured to receive a first waveform encoded signal having a spectral composition up to a first transition frequency, a second waveform encoded signal having a spectral composition corresponding to a subset the frequency range above the first transition frequency, and the parameters of the high-frequency reconstruction; a high-frequency reconstruction unit configured to receive a first waveform-decoded signal and high-frequency reconstruction parameters from a reception unit and to perform a high-frequency reconstruction using a first waveform-encoded signal and high-frequency reconstruction parameters to generate a frequency-expanded signal having a spectral composition above the first frequency transition; and an interleaving unit configured to receive a frequency-expanded signal from a high-frequency reconstruction unit and a second wave-encoded signal from a reception and interleaving unit of a frequency-expanded signal with a second wave-encoded signal.

According to exemplary embodiments, the decoder may be configured to implement any decoding method disclosed herein.

II. Overview - Encoder

According to a second aspect, exemplary embodiments provide encoding methods, encoding devices, and computer program products for encoding. The proposed methods, devices and computer software products, in General, can have the same features and advantages.

The advantages regarding the features and settings presented in the above overview of the decoder, in general, may be suitable for the corresponding features and settings for the encoder.

According to exemplary embodiments, an encoding method is provided in an audio signal processing system, comprising the steps of: receiving an audio signal to be encoded; calculating, based on the received audio signal, the parameters of the high-frequency reconstruction, allowing high-frequency reconstruction of the received audio signal above the first transition frequency; identification, based on the received audio signal, a subset of the frequency range above the first transition frequency, for which the spectral composition of the received audio signal is subject to waveform coding, and then, at the decoder, interleaving with high-frequency reconstruction of the audio signal; generating a first waveform encoded signal by encoding the received audio signal for the spectral bands up to a first transition frequency in a waveform; and a second waveform encoded signal by waveform coding of the received audio signal for spectral bands corresponding to the identified subset of the frequency range above the first transition frequency.

According to exemplary embodiments, a subset of the frequency range above the first transition frequency may comprise a plurality of isolated frequency intervals.

According to exemplary embodiments, a subset of the frequency range above the first transition frequency may comprise a frequency interval extending between the first transition frequency and the second transition frequency.

According to exemplary embodiments, the second transition frequency may vary as a function of time.

According to exemplary embodiments, high-frequency reconstruction parameters are calculated using spectral band copy coding, SBR.

According to exemplary embodiments, the encoding method may further comprise adjusting the spectral envelope levels contained in the high-frequency reconstruction parameters to compensate for summing the high-frequency reconstruction of the received audio signal with the second waveform encoded signal at the decoder. Since the second waveform encoded signal is added to the high frequency reconstructed signal at the decoder, the spectral envelope levels of the combined signal are different from the spectral envelope levels of the high frequency reconstructed signal. This change in the spectral envelope levels can be calculated at the encoder, so that the combined signal at the decoder receives the target spectral envelope. Thanks to the adjustment on the encoder side, the need for intelligence on the decoder side can be reduced, in other words; the need for specifying specific rules for processing the situation on the decoder is eliminated by specific signaling from the encoder to the decoder. This makes it possible to optimize the system in the future with future encoder optimizations without the need for updating potentially widespread decoders.

According to illustrative embodiments, the step of adjusting the parameters of the high-frequency reconstruction may comprise: measuring the energy of a second waveform encoded signal; and adjusting the spectral envelope levels for controlling the spectral envelope of the high frequency reconstructed signal by subtracting the measured energy of the second waveform encoded signal from the spectral envelope levels for the spectral bands corresponding to the spectral compositions of the second waveform encoded signal.

According to exemplary embodiments, a computer program product is also provided comprising a computer-readable medium with instructions for implementing any method of encoding the second aspect.

According to exemplary embodiments, there is provided an encoder for an audio signal processing system, comprising: a receiving unit configured to receive an audio signal to be encoded; a high-frequency coding unit, configured to receive an audio signal from a reception and calculation unit, based on the received audio signal, high-frequency reconstruction parameters allowing high-frequency reconstruction of the received audio signal above the first transition frequency; an interleaved encoding detection unit configured to identify, based on the received audio signal, a subset of the frequency range above the first transition frequency for which the spectral composition of the received audio signal is to be encoded in waveform, and then, at the decoder, interleaved with high-frequency reconstruction of the audio signal; and a waveform coding unit adapted to receive an audio signal from a reception unit and generate a first waveform encoded signal by coding a received audio signal for spectral bands up to a first transition frequency; and receiving an identified subset of the frequency range above the first transition frequency from the interleaved coding detection unit and generating a second waveform encoded signal by encoding the received audio signal for the spectral bands corresponding to the received identified subset of the frequency range.

According to exemplary embodiments, the encoder may further comprise an envelope adjusting unit adapted to receive high-frequency reconstruction parameters from the high-frequency encoding unit and an identified subset of the frequency range above the first transition frequency from the alternating encoding detection unit, and, based on the received data, adjusting the high-frequency parameters reconstruction to compensate for the subsequent interleaving of the high-frequency reconstruction of the received audio signals Ala with the second waveform encoded signal at the decoder.

According to exemplary embodiments, the decoder may be configured to implement any decoding method disclosed herein.

III. Illustrative Embodiments — Decoder

FIG. 1 shows an illustrative embodiment of a decoder 100. The decoder comprises a receiving unit 110, a high frequency reconstruction unit 120, and an interleaving unit 130.

The operation of the decoder 100 will be explained in more detail with reference to the illustrative embodiment shown in FIG. 2, showing the decoder 200, and the flowchart shown in FIG. 3. The purpose of the decoder 200 is to provide improved signal reconstruction for high frequencies in the presence of strong tonal components in the high frequency bands of the audio signal to be reconstructed. The receiving unit 110 receives, in step D02, the first waveform encoded signal 201. The first waveform encoded signal 201 has a spectral composition up to a first transition frequency f _c , i.e. the first waveform encoded signal 201 is a low band signal that is limited to a frequency range below the first transition frequency f _c .

The receiving unit 110 receives, in step D04, a second waveform encoded signal 202. The second waveform encoded signal 202 has a spectral composition that corresponds to a subset of the frequency range above the first transition frequency f _c . In the example of FIG. 2, the second waveform encoded signal 202 has a spectral composition corresponding to a plurality of isolated frequency intervals 202a and 202b. Thus, the second waveform encoded signal 202 can be considered as consisting of a plurality of limited band signals, each limited band signal corresponding to one of the isolated frequency intervals 202a and 202b. In FIG. 2, only two frequency intervals 202a and 202b are shown. In general, the spectral composition of the second waveform encoded signal may correspond to any number of frequency intervals of variable width.

The receiving unit 110 may receive the first and second waveform encoded signals 201 and 202 as two separate signals. Alternatively, the first and second waveform encoded signals 201 and 202 may form first and second signal portions of a common signal received by the reception unit 110. In other words, the first and second waveform encoded signals can be jointly encoded, for example using the same MDCT transform.

Typically, the first waveform encoded signal 201 and the second waveform encoded signal 202 received by the reception unit 110 are encoded using a transform based on overlapping windows, for example, an MDCT transform. The receiving unit may comprise a waveform decoding unit 240 configured to convert the first and second waveform encoded signals 201 and 202 into a time domain. The waveform decoding unit 240 typically comprises a set of MDCT filters configured to inverse transform the MDCTs of the first and second waveform encoded signals 201 and 202.

The receiving unit 110 further receives, at step D06, the high-frequency reconstruction parameters that are used by the high-frequency reconstruction unit 120, as will be described below.

The first waveform encoded signal 201 and the high-frequency parameters received by the receiving unit 110 are then fed to the high-frequency reconstruction unit 120. High frequency reconstruction unit 120 typically operates on signals in the frequency domain, preferably in the QMF region. Therefore, before the high-frequency reconstruction block 120 arrives, the first waveform encoded signal 201 is preferably converted to the frequency domain, preferably the QMF region, by the QMF analysis block 250. The QMF analysis unit 250 typically comprises a QMF filter set configured to perform QMF conversion of the first waveform encoded signal 201.

Based on the first waveform encoded signal 201 and the high-frequency reconstruction parameters, the high-frequency reconstruction unit 120, in step D08, expands the first waveform encoded signal 201 by frequencies above the first transition frequency f _c . In particular, high-frequency reconstruction unit 120 generates the extended frequency signal 203, which has a spectral content higher than the first frequency f _c of the transition. The frequency expanded signal 203 is thus a high band signal.

The high-frequency reconstruction unit 120 may act according to any known algorithm for performing the high-frequency reconstruction. In particular, the high frequency reconstruction unit 120 may be configured to perform SBR as disclosed in a review article by Brinker et al., An overview of the Coding Standard MPEG-4 Audio Amendments 1 and 2: HE-AAC, SSC, and HE-AAC v2 , EURASIP Journal on Audio, Speech, and Music Processing, Volume 2009, Article ID 468971. Thus, a high-frequency reconstruction unit may contain several sub-stages, which are capable of generating an extended frequency signal 203 in several stages. For example, the high-frequency reconstruction unit 120 may include a high-frequency generation unit 221, a parametric high-frequency component summing unit 222, and an envelope adjustment unit 223.

In short, the high frequency generating unit 221, the first sub-step D08a, expands by first coded waveform signal 201 to a range of frequencies above the transition frequency f _c to generate extended frequency signal 203 generated by selecting the first coded sub-band portions of the signal waveform 201 and according to specific rules, in accordance with the parameters of high-frequency reconstruction, duplication or copying of selected sections of the sub-band of the first waveform encoded signal wave 201 to the selected the subband frequency range above the first frequency f _c transition.

The parameters of the high-frequency reconstruction may additionally contain the parameters of the missing harmonics to add the missing harmonics to the frequency-enhanced signal 203. As discussed above, the missing harmonics should be interpreted as any arbitrary strong tonal part of the spectrum. For example, the parameters of the missing harmonics may contain parameters indicating the frequency and amplitude of the missing harmonics. Based on the parameters of the missing harmonics, the summing block 222 of the parametric high-frequency components generates, in a sub-step D08b, sinusoidal components and adds sinusoidal components to the frequency-expanded signal 203.

The parameters of the high-frequency reconstruction may additionally contain spectral envelope parameters describing the target energy levels of the frequency-expanded signal 203. Based on the parameters of the spectral envelope, in sub-step D08c, the envelope adjustment unit 223 can adjust the spectral composition of the frequency-expanded signal 203, i.e. spectral coefficients of the frequency-expanded signal 203, so that the energy levels of the frequency-expanded signal 203 correspond to the target energy levels described by the spectral envelope parameters.

Then, the frequency-expanded signal 203 from the high-frequency reconstruction unit 120 and the second waveform encoded signal from the reception unit 110 are supplied to the interleaver 130. The interleaver 130 typically operates in the same frequency domain, preferably the QMF region, as the high frequency reconstruction unit 120. Thus, the second waveform encoded signal 202 is typically supplied to the interleaver through the QMF analysis unit 250. Additionally, the second waveform encoded signal 202 is typically delayed by a delay unit 260 to compensate for the time required by the high frequency reconstruction unit 120 to perform the high frequency reconstruction. Thus, the second waveform encoded signal 202 and the frequency-expanded signal 203 will be synchronized, so that the interleaver 130 acts on the signals corresponding to the same time frame.

Then, the interleaver 130, in step D10, interleaves, i.e. combines the second waveform encoded signal 202 with a frequency-spread signal 203 to generate an interleaved signal 204. Different approaches can be used to interleave the second wave-encoded signal 202 with a frequency-spread signal 203.

According to one illustrative embodiment, the interleaver 130 interleaves the frequency-expanded signal 203 with the second wave-encoded signal 202 by summing the frequency-expanded signal 203 and the second wave-encoded signal 202. The spectral compositions of the second wave-encoded signal 202 overlap with spectral compositions of the frequency-expanded signal 203 in a subset of the frequency range corresponding to the spectral compositions of the second waveform-encoded signal 202. Bl bestow summation extended frequency signal 203 and the second encoded signal by waveform 202, the interleaved signal 204 thus contains the spectral compositions of the extended frequency signal 203 and the encoded second spectral compositions of the signal waveform 202 for overlapping frequencies. As a result of the summation, the spectral envelope levels of the interleaved signal 204 increase for overlapping frequencies. Preferably, as will be described below, the increase in spectral envelope levels due to summation is calculated on the encoder side when determining the energy envelope levels contained in the high-frequency reconstruction parameters. For example, spectral envelope levels for overlapping frequencies may decrease on the encoder side by an amount corresponding to an increase in spectral envelope levels due to interleaving on the decoder side.

Alternatively, the increase in spectral envelope levels due to summation can be calculated on the side of the decoder. For example, you can provide an energy measuring unit that measures the energy of the second waveform encoded signal 202, compares the measured energy with the target energy levels described by the spectral envelope parameters, and adjusts the frequency-expanded signal 203 so that the spectral envelope levels for the interleaved signal 204 were equal to target energy levels.

According to another exemplary embodiment, the interleaver 130 interleaves the frequency-expanded signal 203 with a second wave-encoded signal 202 by replacing the spectral compositions of the frequency-expanded signal 203 with the spectral compositions of the second wave-encoded signal 202 for those frequencies where the frequency-expanded signal 203 and the second waveform encoded signal 202 is overlapped. In illustrative embodiments, where the frequency expanded signal 203 is replaced by the second waveform encoded signal 202, it is not necessary to adjust the spectral envelope levels to compensate for the alternation of the frequency expanded signal 203 and the second waveform encoded signal 202.

The high-frequency reconstruction unit 120 preferably operates at a sampling rate that is equal to the sampling rate of a lower-level base encoder that was used to encode the first waveform encoded signal 201. Thus, the same transform can be used to encode the second waveform encoded signal 202 based on overlapping windows, for example, the same MDCT that was used to encode the first waveform encoded signal 202.

The interleaver 130 may further be configured to receive a first waveform encoded signal 201 from a reception unit, preferably through a waveform decoding unit 240, a QMF analysis unit 250 and a delay unit 260, and to combine the interleaved signal 204 with the first waveform encoded signal 201 to generate a combined signal 205 having a spectral composition for frequencies below and above the first transition frequency.

Then, the output of the interleaver 130, i.e. the interleaved signal 204 or the combined signal 205, using the QMF synthesis unit 270, can be converted back to the time domain.

Preferably, the QMF analysis unit 250 and the QMF synthesis unit 270 have the same number of subbands, in the sense that the sampling frequency of the signal supplied to the QMF analysis unit 250 is equal to the sampling frequency of the signal output from the QMF synthesis unit 270. As a result, the waveform encoder (using MDCT), which was used to waveform the first and second waveform-encoded signals, can operate at the same sampling frequency as the output signal. Thus, the first and second waveform encoded signals can be efficiently and structurally encoded using the same MDCT transform. This is different from the prior art, where the sampling rate of the waveform encoder is usually limited to half the sampling frequency of the output signal, and the subsequent high-frequency reconstruction module performs up-sampling as well as high-frequency reconstruction. This limits the ability to code in waveform frequencies covering the entire output frequency range.

FIG. 4 illustrates an exemplary embodiment of a decoder 400. Decoder 400 is designed to provide improved signal reconstruction for high frequencies in the presence of transients in the input audio signal to be reconstructed. The main difference between the example shown in FIG. 4 and the example shown in FIG. 2, consists in the form of spectral composition and the duration of the second waveform encoded signal.

FIG. 4 shows the operation of decoder 400 over a plurality of consecutive time slots of a time frame; in this case, three consecutive time sections are shown. A time frame may correspond, for example, to 2048 time samples.

In particular, during the first time portion, the receiving unit 110 receives a first waveform encoded signal 401a having a spectral composition up to a first transition frequency f _c1 . A second waveform encoded signal is not received during the first time portion.

During the second time period, the receiving unit 110 receives a first waveform encoded signal 401b having a spectral composition up to a first transition frequency f _c1 , and a second waveform encoded signal 402b having a spectral composition that corresponds to a subset of a frequency range above a first frequency f _c1 transition. In the example of FIG. 4, the second waveform encoded signal 402b has a spectral composition corresponding to a frequency interval passing between the first transition frequency f _c1 and the second transition frequency f _C2 . Thus, the second waveform encoded signal 402b is a limited band signal limited by the frequency band between the first transition frequency f _c1 and the second transition frequency f _C2 .

During the third portion temporarily receiving unit 110 receives the first encoded waveform 401c of a signal having a spectral content to a first transition frequency f _c1. During the third time portion, a second waveform encoded signal is not received.

Throughout the illustrated first and third time sections, there are no second waveform encoded signals. During these time sections, the decoder will operate as a traditional decoder configured to perform high-frequency reconstruction, for example, a traditional SBR decoder. The high frequency reconstruction unit 120 will generate frequency-expanded signals 403a and 403c based on the first waveform-encoded signals 401a and 401c, respectively. However, since there are no second waveform encoded signals, the interleaving will not be performed by the interleaving unit 130.

During the illustrated second time portion, a second waveform encoded signal 402b is present. During the second time portion, the decoder 400 will operate in the same manner as described with respect to FIG. 2. In particular, the high-frequency reconstruction unit 120 performs the high-frequency reconstruction based on the first waveform-encoded signal and the high-frequency reconstruction parameters to generate a frequency-expanded signal 403b. Then, the frequency-expanded signal 403b is supplied to an interleaver 130, where it is interleaved with a second waveform-encoded signal 402b to form an interleaved signal 404b. As discussed in connection with the illustrative embodiment shown in FIG. 2, interleaving can be carried out using an add or replace approach.

In the above example, during the first and third time sections of the second waveform encoded signal does not exist. During these time sections, the second transition frequency is equal to the first transition frequency, and interleaving is not performed. During the second time frame, the second transition frequency is greater than the first transition frequency, and interleaving is performed. In general, the second transition frequency may thus vary as a function of time. In particular, the second transition frequency may vary in a time frame. Interleaving will occur when the second transition frequency is greater than the first transition frequency and less than the maximum frequency provided by the decoder. The case when the second transition frequency is equal to the maximum frequency corresponds to the actual encoding according to the waveform, and high-frequency reconstruction is not required.

It should be noted that the embodiments described with respect to FIG. 2 and 4, can be combined. FIG. 7 shows a time-frequency matrix 700 defined with respect to a frequency domain, preferably a QMF region, in which an interleaver 130 interleaves. The illustrated time-frequency matrix 700 corresponds to one frame of an audio signal to be decoded. The illustrated matrix 700 is divided into 16 time slots and a plurality of frequency subbands, starting from the first transition frequency f _c1 . Additionally shown are a first time range T ₁ spanning a time range below an eighth time slot, a second time range T ₂ spanning an eighth time slot, and a time range T ₃ spanning time slots above an eighth time slot. Different spectral envelopes, as part of the SBR data, may be associated with different time ranges T ₁ - T ₃ .

In the present example, two strong tonal components in the frequency bands 710 and 720 are identified in the audio signal on the encoder side. The frequency bands 710 and 720 may have the same bandwidth as, for example, SBR envelope bands, i.e. the same frequency resolution that is used to represent the spectral envelope. These tonal components in bands 710 and 720 have a time range corresponding to the full time frame, i.e. the time range of the tonal components includes the time ranges T ₁ - T ₃ . On the encoder side, it is decided to waveform the tonal components of the bands 710 and 720 during the first time range T ₁ , illustrated by the tonal components 710a and 720, hatched over the first time range T ₁ . Additionally, on the encoder side, it is decided that, during the second and third time ranges T ₂ and T ₃ , the first tonal component 710 needs to be parametrically reconstructed at the decoder by turning on a sine wave, as explained in connection with the summing block 222 of the parametric high-frequency components shown in FIG. 2. This is illustrated by the square pattern of the first tonal component 710b over the (second time range T ₂ ) and the third time range T ₃ . During the second and third time ranges T ₂ and T ₃ , the second tonal component 720 is still encoded in waveform. Additionally, in this embodiment, the first and second tonal components are interleaved with the high-frequency reconstructed audio signal by adding, and thus, the encoder adjusts the transmitted spectral envelope, the SBR envelope, respectively.

Additionally, transient 730 is identified in the audio signal on the encoder side. Transient 730 has a time duration corresponding to a second time range T ₂ and corresponds to a frequency interval between a first transition frequency f _c1 and a second transition frequency f _C2 . On the encoder side, a decision is made to encode, in waveform, the time-frequency portion of the audio signal corresponding to the transient position. In this embodiment, the interleaving of the waveform encoded transient is done by replacement. The signaling circuit is designed to signal this information to the decoder. The signaling circuit contains information indicating in which time ranges and / or in which frequency ranges above the first transition frequency f _c1 a second waveform encoded signal is available. The signaling scheme may also be associated with rules indicating how interleaving should be performed, i.e., whether interleaving should be performed by adding or replacing. The signaling scheme may also be associated with rules defining the priority order of adding or replacing different signals, which will be explained below.

The signaling circuit includes a first vector 740, designated an “additional sine wave”, indicating for each subband whether to add a sine wave parametrically or not. In FIG. 7, the summation of the first tonal component 710b in the second and third time ranges T ₂ and T _{3 is} indicated by “1” for the corresponding subband of the first vector 740. Signaling including the first vector 740 is known in the art. In a traditional decoder, rules are set when a sine wave is allowed to start. The rule is that if a new sine wave is detected, i.e. the “additional sine wave” signaling of the first vector 740 changes from zero in one frame to one in the next frame, over a specific subband, then the sine wave starts at the beginning of the frame if there is no transition event in the frame for which the sine wave starts at the moment of transition. In the illustrated example, a transition event 730 occurs in the frame, explaining why the parametric reconstruction by a sine wave for the frequency band 710 begins only after the transition event 730.

The signaling circuit further includes a second vector 750, designated “waveform coding”. The second vector 750 indicates for each subband whether the waveform encoded signal is available for interleaving with high-frequency reconstruction of the audio signal. In FIG. 7, the availability of the waveform encoded signal for the first and second tone components 710 and 720 is indicated by “1” for the corresponding subband of the second vector 750. In the present example, an indication of the availability of waveform encoded data in the second vector 750 is also an indication that the interleaving to be implemented by adding. However, in other embodiments, the indication of the availability of waveform encoded data in the second vector 750 may be an indication that the interleaving is to be implemented by replacement.

The signaling circuit further includes a third vector 760, designated “waveform coding”. A third vector 760 indicates for each time slot whether the waveform encoded signal is available for interleaving with high frequency reconstruction of the audio signal. In FIG. 7, the availability of the waveform encoded signal for transient 730 is indicated by “1” for the corresponding time slot of the third vector 760. In the present example, an indication of the availability of waveform encoded data in the third vector 760 is also an indication that the interleaving is to be performed by replacement . However, in other embodiments, an indication of the availability of waveform encoded data in the third vector 760 may be an indication that the interleaving is to be done by adding.

There are many alternatives for implementing the first, second, and third vectors 740, 750, 760. In some embodiments, vectors 740, 750, 760 are binary vectors that use a logical zero or logical unit to provide their indications. In other embodiments, vectors 740, 750, 760 may take various forms. For example, a first value, such as “0” in a vector, may indicate that waveform-encoded data is not available for a particular frequency band or time slot. A second value, such as “1” in a vector, may indicate that interleaving is to be done by adding for a specific frequency band or time slot. A third value, such as “2” in a vector, may indicate that interleaving is to be done by substituting for a particular frequency band or time slot.

The above illustrative signaling scheme may also be associated with a priority order that may be applied in case of conflict. By way of example, a third vector 760 representing interleaving the transient by replacement may take precedence over the first and second vectors 740 and 750. Additionally, the first vector 740 may take precedence over the second vector 750. It should be understood that any priority order can be set between vectors 740, 750, 760.

FIG. 8a shows in more detail the interleaver 130 shown in FIG. 1. The interleaver 130 may comprise a signal decoding component 1301, a decision logic component 1302, and an interleaving component 1303. As discussed above, the interleaver 130 receives a second waveform encoded signal 802 and a frequency-expanded signal 803. The interleaver 130 may also receive a control signal 805. The signal decoding component 1301 decodes a control signal 805 into three parts corresponding to a first vector 740, a second vector 750, and a third vector 760 of the signaling circuit described with respect to FIG. 7. They are sent to the decision logic component 1302, which, based on the logic, creates a time-frequency matrix 870 for the QMF frame, indicating which of the second waveform encoded signal 802 and the frequency-expanded signal 803 should be used for which time-frequency mosaic element. The time-frequency matrix 870 is sent to the interleaving component 1303 and is used to interleave the second waveform encoded signal 802 with a frequency-expanded signal 803.

The decision logic component 1302 is shown in more detail in FIG. 8b. The decision logic components 1302 may include a time-frequency matrix generation component 13021 and a priority assignment component 13022. The time-frequency matrix generating component 13021 generates a time-frequency matrix 870 having time-frequency mosaic elements corresponding to the current QMF frame. The time-frequency matrix generating component 13021 includes information from a first vector 740, a second vector 750, and a third vector 760 in a time-frequency matrix. For example, as shown in FIG. 7, in the presence of “1” (or, in a more general case, any number other than zero) in the second vector 750 for a certain frequency, the time-frequency mosaic elements corresponding to a certain frequency are set to “1” (or, in more in general, the number present in vector 750) in the time-frequency matrix 870 indicating that the interleaving with the second waveform encoded signal 802 is to be performed for these time-frequency mosaic elements. Similarly, if there is “1” (or, in a more general case, any number other than zero) in the third vector 760 for a specific time slot, the time-frequency mosaic elements corresponding to the specific time slot are set to “1” (or, more generally, to any number other than zero) in the time-frequency matrix 870 indicating that the interleaving with the second waveform encoded signal 802 is to be performed for these time-frequency mosaic elements. Similarly, if there is “1” in the first vector 740 for a specific frequency, the time-frequency mosaic elements corresponding to the specific frequency are set to “1” in the time-frequency matrix 870, indicating that the output signal 804 should be based on a frequency-expanded signal 803, in which a certain frequency is parametrically reconstructed, for example by turning on a sinusoidal signal.

For some time-frequency mosaic elements, a conflict occurs between the information from the first vector 740, the second vector 750 and the third vector 760, in the sense that more than one of the vectors 740-760 indicates a non-zero number, for example “1”, for the same time-frequency mosaic element of the time-frequency matrix 870. In such a situation, the priority assignment component 13022 needs to decide how to prioritize information from the vectors to eliminate conflicts in the time-frequency matrix 870. More precisely in other words, the priority assignment component 13022 decides whether the output signal 804 should be based on the frequency-expanded signal 803 (thus giving priority to the first vector 740) by interleaving the second waveform encoded signal 802 in the frequency direction (thus giving priority to the second vector 750), or by interleaving the second waveform encoded signal 802 in the time direction (thus giving priority to the third vector 750).

To this end, the priority assignment component 13022 contains predefined rules indicating the priority order of vectors 740-760. Priority assignment component 13022 may also include predefined rules indicating how interleaving should be performed, i.e. whether interleaving by adding or replacing.

Preferably, these rules are as follows:

interleaving in the time direction, i.e. the interleaving given by the third vector 760 is given the highest priority. The interleaving in the time direction is preferably carried out by replacing the frequency-expanded signal 803 in those time-frequency mosaic elements defined by the third vector 760. The time resolution of the third vector 760 corresponds to the time slot of the QMF frame. If the QMF frame corresponds to 2048 time-domain samples, the time slot can typically correspond to 128 time-domain samples;

parametric reconstruction of frequencies, i.e. the use of a frequency-expanded signal 803 specified by the first vector 740 is given the second after the highest priority. The frequency resolution of the first vector 740 is the frequency resolution of the QMF frame, for example, the SBR envelope band. Traditional rules indicating signaling and interpretation of the first vector 740 are still valid;

interleaving in the frequency direction, i.e. the interleaving given by the second vector 750 is given the lowest priority order. Interleaving in the frequency direction is carried out by adding a frequency-expanded signal 803 to those time-frequency mosaic elements defined by the second vector 750. The frequency resolution of the second vector 750 corresponds to the frequency resolution of the QMF frame, for example, the SBR envelope band.

III. Illustrative Embodiments - Encoder

FIG. 5 shows an illustrative embodiment of an encoder 500 that is suitable for use in an audio processing system. The encoder 500 comprises a reception unit 510, a waveform encoding unit 520, a high frequency encoding unit 530, an interleaving encoding detection unit 540, and a transmission unit 550. The high-frequency coding unit 530 may include a high-frequency reconstruction parameter calculation unit 530a and a high-frequency reconstruction parameter adjustment unit 530b.

The operation of the encoder 500 will be described hereinafter with reference to FIG. 5 and in the flowchart of FIG. 6. At step E02, the receiving unit 510 receives the audio signal to be encoded.

The received audio signal is sent to the block 530 high-frequency coding. Based on the received audio signal, the high-frequency coding unit 530 and, in particular, the high-frequency reconstruction parameter calculating unit 530a, calculates in step E04 high-frequency reconstruction parameters allowing high-frequency reconstruction of the received audio signal above the first transition frequency f _c . The high-frequency reconstruction parameter calculation unit 530a may use any known method to calculate the high-frequency reconstruction parameters, for example, SBR coding. The high frequency coding unit 530 typically operates in the QMF domain. Thus, before calculating the parameters of the high-frequency reconstruction, the high-frequency coding unit 530 can perform QMF analysis of the received audio signal. As a result, high-frequency reconstruction parameters are set with respect to the QMF region.

The calculated parameters of the high-frequency reconstruction may contain several parameters related to the high-frequency reconstruction. For example, high-frequency reconstruction parameters may include parameters indicating how to duplicate or copy an audio signal from sections of a subband of a frequency range below a first frequency f _{c of a} transition to sections of a subband of a frequency range above a first frequency f _{c of a} transition. Such parameters are sometimes referred to as parameters describing the patch structure.

The parameters of the high-frequency reconstruction may further comprise spectral envelope parameters describing the target energy levels of the sub-band sections of the frequency range above the first transition frequency.

The high-frequency reconstruction parameters may additionally contain the parameters of the missing harmonics indicating harmonics, or strong tonal components that will disappear if the audio signal is reconstructed in the frequency range above the first transition frequency using parameters describing the patch structure.

Then, the interleaved coding detection unit 540, in step E06, identifies a subset of the frequency range above the first transition frequency f _c for which the spectral composition of the received audio signal is subject to waveform coding. In other words, the interleaved coding detection unit 540 is used to identify frequencies above the first transition frequency for which high-frequency reconstruction does not produce the desired result.

The interleaved encoding detection unit 540 may take various approaches to identify the desired subset of the frequency range above the first transition frequency f _c . For example, the interleaved coding detection unit 540 may identify strong tonal components that cannot be reconstructed well by high frequency reconstruction. The identification of strong tonal components can be based on the received audio signal, for example, by determining the energy of the audio signal as a function of frequency and identifying frequencies having high energy as containing strong tonal components. Additionally, the identification may be based on knowledge of how the received audio signal will be reconstructed at the decoder. In particular, such identification can be based on tonality quotas, which are expressed as the ratio of the tonality measures of the received audio signal and the tonality measures of the reconstruction of the received audio signal for frequency bands above the first transition frequency. A high tone quota indicates that the audio signal will not be successfully reconstructed for a frequency corresponding to the tone quota.

The interleaved encoding detection unit 540 may also detect transients in the received audio signal that cannot be reconstructed well by high-frequency reconstruction. Such identification may be the result of a time-frequency analysis of the received audio signal. For example, the time-frequency interval where the transient occurs can be detected from the spectrogram of the received audio signal. Such a time-frequency interval typically has a time range that is shorter than the time frame of the received audio signal. The corresponding frequency range usually corresponds to a frequency interval that extends to a second transition frequency. Therefore, a subset of the frequency range above the first transition frequency can be identified by the interleaving coding detection unit 540 as an interval from the first transition frequency to the second transition frequency.

The interleaved encoding detection unit 540 may further receive high-frequency reconstruction parameters from the high-frequency reconstruction parameter calculation unit 530a. Based on the parameters of the missing harmonics from the parameters of the high-frequency reconstruction, the interleaved coding detection unit 540 can identify the frequencies of the missing harmonics and decide to include at least some of the frequencies of the missing harmonics in the identified subset of the frequency range above the first transition frequency f _c . This approach may be advantageous if there is a strong tonal component in the audio signal that cannot be accurately modeled within the parametric model.

The received audio signal is also fed to the waveform coding unit 520. The waveform coding unit 520, in step E08, performs waveform coding of the received audio signal. In particular, the waveform coding unit 520 generates a first waveform encoded signal by waveform coding an audio signal for spectral bands up to a first transition frequency f _c . Additionally, the waveform coding unit 520 receives the identified subset from the interleaved encoding detection unit 540. Then, the waveform coding unit 520 generates a second waveform encoded signal by waveform coding the received audio signal for the spectral bands corresponding to the identified subset of the frequency range above the first transition frequency. For this reason, the second waveform encoded signal will have a spectral composition corresponding to the identified subset of the frequency range above the first transition frequency f _c .

According to exemplary embodiments, the waveform coding unit 520 can generate first and second waveform encoded signals, first encoding the received audio signal for all spectral bands in waveform, and then removing the spectral composition of the waveform encoded signal for frequencies corresponding to the identified subset frequencies above the first frequency f _c transition.

The waveform coding unit may, for example, perform waveform coding using a set of transform filters based on overlapping windows, for example, an MDCT filter set. Such sets of conversion filters based on overlapping windows use windows having a certain time extent, so that the signal values in the previous and next time frames affect the values of the converted signal in one time frame. To mitigate this effect, it may be advantageous to carry out a certain amount of time transcoding, in the sense that the waveform coding unit 520 not only encodes the current time frame of the received audio signal, but also the previous and next time frames of the received audio signal. Similarly, the high-frequency coding unit 530 can also encode not only the current time frame of the received audio signal, but also the previous and next time frames of the received audio signal. Thus, in the QMF region, an improved wiring transition between the second waveform encoded signal and the high frequency reconstruction of the audio signal can be achieved. Additionally, this eliminates the need to adjust the boundaries of the spectral envelope data.

It should be noted that the first and second waveform encoded signals may be separate signals. However, it is preferred that they form portions of the first and second waveform encoded signals from a common signal. If so, they can be generated by performing a single waveform encoding operation on a received audio signal, for example, by applying a single MDCT transform to a received audio signal.

The high-frequency coding unit 530, and in particular the high-frequency reconstruction parameter adjusting unit 530b, can also receive an identified subset of the frequency range above the first transition frequency f _c . Based on the received data, the high-frequency reconstruction parameter adjustment unit 530b, in step E10, can adjust the high-frequency reconstruction parameters. In particular, the high-frequency reconstruction parameter adjustment unit 530b may adjust the high-frequency reconstruction parameters corresponding to the spectral bands contained in the identified subset.

For example, the high-frequency reconstruction parameter adjusting unit 530b may adjust the spectral envelope parameters describing the target energy levels of the sub-band sections of the frequency range above the first transition frequency. This is especially significant if the second waveform-encoded signal needs to be summed with the high-frequency reconstruction of the audio signal at the decoder, since then the energy of the second wave-encoded signal will be summed with the energy of the high-frequency reconstruction. To compensate for this summation, the high-frequency reconstruction parameter adjustment unit 530b can adjust the energy envelope parameters by subtracting the measured energy of the second waveform encoded signal from the target energy levels for the spectral bands corresponding to the identified subset of the frequency range above the first transition frequency f _c . Thus, the total energy of the signal will be preserved by summing the second waveform encoded signal and high-frequency reconstruction at the decoder. The energy of the second waveform encoded signal may be measured, for example, by interleaving coding detection unit 540.

The high-frequency reconstruction parameter adjustment unit 530b may also adjust the parameters of the missing harmonics. In particular, if the subband containing the missing harmonics indicated by the parameters of the missing harmonics is part of the identified subset of the frequency range above the first transition frequency f _c , then the subband will be encoded in waveform by waveform encoding unit 520. Thus, the high-frequency reconstruction parameter adjustment unit 530b can remove such missing harmonics from the parameters of the missing harmonics, since such missing harmonics need not be parametrically reconstructed on the decoder side.

Then, the transmission unit 550 receives the first and second waveform encoded signals from the waveform encoding unit 520 and the high-frequency reconstruction parameters from the high-frequency encoding unit 530. Transmission unit 550 formats the received data in a bitstream for transmission to a decoder.

The interleaved encoding detection unit 540 may further signal information to the transmit unit 550 for inclusion in the bitstream. In particular, the interleaved encoding detection unit 540 can signal how to interleave a second waveform encoded signal with high-frequency reconstruction of the audio signal, for example, whether interleaving is performed by adding signals or by replacing one of the signals with another, and for which frequency range and what interval time should be interleaved waveform encoded signals. For example, signaling may be performed using the signaling scheme discussed with reference to FIG. 7.

Equivalents, extensions, alternatives, etc.

Additional embodiments of the present invention will become apparent to a person skilled in the art after studying the above description. Although embodiments and examples are disclosed in the present description and drawings, the invention is not limited to these specific examples. Numerous modifications and variations may be proposed without departing from the scope of the present invention as defined by the appended claims. No reference position given in the claims should not be understood in order to limit its scope.

Additionally, one skilled in the art can understand and implement variations of the disclosed embodiments, practicing the invention, studying the drawings, disclosure, and the following claims. In the claims, the word “comprising” does not exclude the presence of other elements or steps, and the use of their names in the singular does not exclude the presence of many of them. The mere fact that certain measures are mentioned in mutually different dependent clauses does not mean that a combination of these measures cannot be used to advantage.

The systems and methods disclosed above can be implemented as software, firmware, hardware, or a combination thereof. In a hardware implementation, the distribution of tasks between the functional blocks mentioned in the above description does not necessarily correspond to the division into physical blocks; on the contrary, one physical component can have several functionalities, and one task can be jointly carried out by several physical components. Certain components, or all components, can be implemented as software executed by a digital signal processor or microprocessor, or implemented as hardware or as a specialized integrated circuit. Such software may be distributed on computer-readable media that may contain computer storage media (or non-transient media) and transmission media (or transit media). As is well known to a person skilled in the art, the term "computer storage media" includes volatile and non-volatile, removable and fixed media implemented by any method or technology for storing information, for example, computer-readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVDs) or other optical disk storage devices, magnetic tapes, magnetic tape, magnetic disk a storage device or other magnetic storage devices, or any other medium that can be used to store the necessary information and which can be accessed by a computer. Additionally, one skilled in the art is well aware that communication media typically embody computer-readable instructions, data structures, program modules or other data in a modulated data signal, for example, a carrier wave or other transfer mechanism, and include any delivery media information.

Claims (35)

1. A method of decoding an audio signal in an audio processing system, comprising the steps of: receive a first waveform encoded signal having a spectral composition up to a first transition frequency, receiving a second waveform encoded signal having a spectral composition corresponding to a subset of the frequency range above the first transition frequency, wherein the subset of the frequency range above the first transition frequency includes an isolated frequency interval not adjacent to the spectral composition of the first waveform encoded signal, accept high-frequency reconstruction parameters, performing high-frequency reconstruction using at least a portion of the first waveform-encoded signal and high-frequency reconstruction parameters in order to generate a frequency-expanded signal having a spectral composition higher than the first transition frequency, and interleaving a frequency-expanded signal with a second waveform encoded signal, wherein the audio processing system is implemented, at least in part, using hardware. 2. The decoding method according to claim 1, wherein the spectral composition of the second waveform encoded signal has an upper bound that varies with time. 3. The decoding method according to claim 1, further comprising the step of combining a frequency-expanded signal, a second wave-encoded signal and a first wave-encoded signal to generate a full-bandwidth audio signal. 4. The decoding method according to claim 1, wherein the step of performing the high-frequency reconstruction comprises copying the lower frequency band to the higher frequency band. 5. The decoding method according to claim 1, wherein the step of performing the high-frequency reconstruction is carried out in the frequency domain. 6. The decoding method according to claim 1, wherein the step of interleaving the frequency-expanded signal with a second waveform encoded signal is performed in the frequency domain. 7. The decoding method of claim 5, wherein the frequency domain is a region of quadrature mirror filters, QMF. 8. The decoding method of claim 1, wherein the received first and second waveform encoded signals are encoded using the same MDCT transform. 9. The decoding method according to claim 1, further comprising adjusting the spectral composition of the frequency-expanded signal in accordance with high-frequency reconstruction parameters in order to adjust the spectral envelope of the frequency-expanded signal. 10. The decoding method according to claim 1, wherein the interleaving comprises the step of summing the second waveform encoded signal with a frequency-expanded signal. 11. The decoding method according to claim 1, wherein the interleaving comprises replacing the spectral composition of the frequency-expanded signal with the spectral composition of the second waveform encoded signal in a subset of the frequency range above the first transition frequency, which corresponds to the spectral composition of the second waveform encoded signal. 12. The decoding method of claim 1, wherein the first waveform encoded signal and the second waveform encoded signal form the first and second signal portions of the common signal. 13. The decoding method according to claim 1, further comprising the step of: receiving a control signal comprising data relating to one or more time ranges and one or more frequency ranges above the first transition frequency, for which a second waveform encoded signal is available, wherein the step of interleaving the frequency-expanded signal with the second waveform encoded signal is based on the control signal. 14. The decoding method of claim 13, wherein the control signal comprises at least one of a second vector indicating one or more frequency ranges above the first transition frequency for which a second waveform encoded signal is available for interleaving with a frequency-expanded signal, and a third vector indicating one or more time ranges for which a second waveform encoded signal is available for interleaving with a frequency-expanded signal. 15. The decoding method according to claim 13, wherein the control signal comprises a first vector indicating one or more frequency ranges above the first transition frequency to be parametrically reconstructed based on high-frequency reconstruction parameters. 16. A long-term computer-readable medium with instructions that, when executed by a processor, perform the method of claim 1. 17. An audio decoder for decoding an encoded audio signal, the audio decoder comprising: an input interface configured to receive a first waveform encoded signal with spectral composition up to a first transition frequency, a second waveform encoded signal with spectral composition corresponding to a subset of the frequency range above the first transition frequency, as well as high-frequency reconstruction parameters, and a subset of the range frequencies above the first transition frequency includes an isolated frequency interval not adjacent to the spectral composition of the first waveform encoded with I drove; a high-frequency reconstruction unit configured to receive a first waveform-decoded signal and high-frequency reconstruction parameters from the receiving and performing high-frequency reconstruction stage using a first waveform-encoded signal and high-frequency reconstruction parameters in order to generate a frequency-expanded signal having a spectral composition higher than the first transition frequency; an interleaving unit configured to receive a frequency-expanded signal from the high-frequency reconstruction stage and a second wave-encoded signal from the reception and interleaving stage of the frequency-expanded signal with a second wave-encoded signal, wherein the audio decoder is implemented, at least in part, using hardware. 18. A coding method in an audio processing system, comprising the steps of: receive an audio signal to be encoded; calculating, based on the received audio signal, high-frequency reconstruction parameters allowing high-frequency reconstruction of the received audio signal above the first transition frequency, identifying, based on the received audio signal, a subset of the frequency range above the first transition frequency, for which the spectral composition of the received audio signal is to be encoded in waveform, and then, at the decoder, interleaving with high-frequency reconstruction of the audio signal; generating a first waveform encoded signal by waveform coding a received audio signal for spectral bands up to a first transition frequency and a second waveform encoded signal by waveform coding a received audio signal for spectral bands corresponding to an identified subset of a frequency range above a first transition frequency, moreover, a subset of the frequency range above the first transition frequency includes an isolated frequency interval not adjacent to the spectral composition of the first th coded shape signal wave, wherein the audio processing system is implemented, at least in part, using hardware. 19. The encoding method according to claim 18, wherein the spectral composition of the second waveform encoded signal has an upper bound that varies over time. 20. The encoding method of claim 18, wherein the high-frequency reconstruction parameters are calculated using spectral band copy coding, SBR.

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